1. Technical Field
The present invention relates to a waveguide coupling device, and more particularly, to a waveguide coupling device with properties of forward coupling and backward coupling as well as a manufacturing method thereof, used for high efficient waveguide and fiber coupling. The forward coupling is defined by optical wave propagating from an external fiber to a waveguide whereas the backward coupling is defined by optical wave propagating from a waveguide to an external fiber.
2. Description of Related Art
In recent years, since the advancement of network and information transmission, the transmission volume of data completed through Internet has been obviously increased; thus, the traditional data transmission way carried out by a coaxial cable is inadequate for high data throughput. However, compared with the coaxial cable, fibers have several advantages, such as high communication capacity, low signal loss, anti-electromagnetic interference, light weight, and small size; therefore, the fiber has been became the main component used in data transmission.
In addition to fibers, integrated photonic devices used for optical signal processing and high-speed electrical-to-optical or optical-to-electrical conversion also play an important role in the applications of optical interconnect. Integrated photonic devices include active and passive components, wherein the active component is referred to the device which can perform energy conversion, for example, an electro-optic modulator can carry out electro-optical conversion of generating optical signals. The passive component is referred to the device without energy conversion, for instance, waveguide couplers. A waveguide coupler is able to divert the optical power between a waveguide and another waveguide, or between a fiber and the waveguide.
Please refer to FIG. 1, which illustrates a stereo view of a conventional optical waveguide device. As shown in FIG. 1, the optical waveguide device 25′ includes: a substrate 252′, a top layer 254′ and a waveguide layer 256′, wherein the optical wave is propagating in the waveguide layer 256′. The optical waveguide device 25′ shown in FIG. 1 is a butt coupling device and the structure thereof is very simple. Traditionally, the waveguide layer 256′ is rectangle structure, however, for connecting to the fiber, the waveguide layer 256′ is made to circular structure when manufacturing the optical waveguide device 25′. The aforesaid optical waveguide device 25′ can be integrated to a miniaturized structure by using semiconductor materials and related semiconductor process, and that is the main advantage of the optical waveguide device 25′. The main shortcoming of the optical waveguide device 25′ is that the height (thickness) of the waveguide layer 256′ can not be designed too high, so that, it is difficult for the optical waveguide device 25′ to connect with the fiber (the diameter of fiber core is around 8 μm).
Besides, please refer to FIG. 2, which illustrates a stereo view of a conventional optical waveguide device with a surface grating. As shown in FIG. 2, the optical waveguide device 1′ with the surface grating includes: a substrate 2′ and an optical waveguide 3′. The optical waveguide 3′ is formed on a base surface 21′ of the substrate 2′, and has a top surface 31′, a first side surface 32′ and a second side surface 33′. Moreover, a surface grating 4′ is consisted of a plurality of indentations 30′ and formed on the first side surface 32′, wherein the period of the surface grating 4′ is determined by the spacing distance between the plurality of indentations 30′. The aforesaid optical waveguide device 1′ is a surface coupling device, which is able to couple the optical wave with a specific wavelength through the surface grating 4′ thereof, for example, coupling the optical wave with the wavelength 1490 nm. Besides, the period of the surface grating 4′ can be adjusted by changing the spacing distance between the indentations 30′, so as to make the optical waveguide 3′ couple and transmit the optical waves with different wavelengths via the surface grating 4′.
The aforesaid optical waveguide device 1′ has a main advantage, that is, the optical waveguide device 1′ is capable of being changed the period of the periodic surface grating 4′ thereof, such that the optical waveguide device 1′may couple the optical wave with the specific wavelength. Moreover, to prevent from damage occurred in combining the surface grating 4′ with the fiber, a protection layer is formed on the surface grating 4′. However, the formed protection layer reduces the optical coupling efficiency of the optical waveguide device 1′; besides, the surface grating 4′ must achieve phase matching with the optical wave in period when using the optical waveguide device 1′ to couple the optical wave, so that the operation of high-efficiency optical wave coupling can be accomplished. However, such limitation (phase matching) reduces the whole coupling efficiency of the optical waveguide device 1′ for broadband optical wave.
Accordingly, in view of the optical waveguide device (i.e., the butt coupling device with simple structure) and the optical waveguide device with the surface grating (i.e., the surface coupling device capable of coupling the optical wave with the particular wavelength) still have shortcomings and drawbacks, the inventor of the present application has made great efforts to make inventive research thereon and eventually provided a waveguide coupling device with properties of forward coupling and backward coupling as well as a manufacturing method thereof.